Revealing mistake: When Eric is using the guillotine to cut the head off Christi's teddy bear you can see the Velcro attached to the bear's head showing where it is supposed to come off.
Continuity mistake: In some scenes Sebastian is missing a front tooth but in other scenes it is there.
Answer: The skull and crossbone flag can be interpreted in a number of ways. Death, both literally and symbolically, is an ongoing theme in the story. Cedric Brown, the children's father, is a widower, and he is also an undertaker. There have been a number of nannies for Mr. Brown's rather naughty children, but they have systematically gotten rid of each one, basically "killing them off," though not in a literal sense, until Nanny McPhee arrives.
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